Spark plug



Dec. 13, 1938. c. R. BENTON j 2,139,793

SPARK PLUG Filed June 15, 1936 Ju /Z727 Patented Dec. 13, 1938 UNITEDSTATES PATIENT OFFICE SPARK PLUG Cecil B. Benton, Vergennes, Vt.Application an. 15, 1936, Serial No. 85,201

3 Claims.

The inventionrelates to spark plugs. The primary object of the inventionis to pro vide an electrode on the shell of the plug, usually the groundelectrode which can be readily and accurately deformed or varied toprovide the optimum gap for sparking and also shields the sparking faceon the center electrode from direct contact with the flame in thecylinder.

Another object of the invention is to achieve this primary object with adiversity of forms of electrodes, and with spark plugs for engineshaving different output characteristics.

Other objects of the invention will appear from the detaileddescription.

)5 The invention consists in the several novel features which arehereinafter set forth and are more particularly defined by claims at theconclusion hereof. r P

In the drawing: a to Fig. 1 is a longitudinal section of a spark plugembodying one form of the invention;

Fig. 2 is a section, on an enlarged scale,

through the electrodes and shell, illustrating the manner of resettingthe electrode on the shell to 1'3 vary, and provide the optimum gapbetween the a spark plug comprising a shell II), which is provided withthe usual screw-thread for engaging a corresponding internal thread inthe engine cas- 4 ing and with a polygonal flange ll whereby theassembled plug may be screwed into the casing;

a center electrode l2 having a cylindrical termi-' nal l3 at its innerend on which the flat circular sparking face I4 is formed; and a stem 9extending longitudinally through the plug; a sleeve l5 of suitableinsulation surrounding the stem 9 and engaged by a shoulder IE onelectrode l2; a coupling ring l1 provided with a screw-thread I8 50 forengaging a corresponding internal thread in the shell l0 and having ashouldered inner end for engaging a gasket 20 and forcing it against aconoidal surface in the shell; a collar 2| fixed to the outer end of thestem 9 of electrode 12 and 55 for electrical connection with a conductorwire;

and a sleeve 22 of insulation between collar 2| and ring [1.

The-ground contact 24 consists of a strip of metal extending across thecylindrical opening in the inner end of shell ID, with its ends 25seated 5 in recesses cut in the end of the shell and secured therein bybrazing or welding, as indicated at 26. The central portion 21 of thestrip 24 is offset longitudinally of the axis of the inner electrode 12,being bent as at 28 between the portions'25 l0 and 21. The inner face ofofiset portion 21 forms the sparking face of the ground electrode. Theelectrode 24 is shaped from a strip of fiat stock and its centralportion 21 is of sufificient width or area to overlie the sparkingfacel4 on the central electrode l2 so it will shield the sparking face I 4of the central electrode from the'flame in the cylinder and preventscouring of the sparking face I4 by such flame. The central electrode 12is usually made of a spark-resisting alloy of steel, because it isinsulated from the shell and is thus not as well cooled by intimatecontact with the cylinder head. The electrode 24 is formed of a metal,steel or alloy which is suificiently ductile or malleable so as to avoidany spring-action i when it is deformed and so that when it is impactedby a tool, such as a suitable hammer, the central portionj1 will remainset in its deformed shape with practically :no tendency to spring backto its normal shape. This degree of ductility 30 or malleability may beattained by subjecting the 7 metal to suitable heat treatment.v The heatapplied to the ends 25 of the strip, for welding or brazing them to theshell, may be utilized to some extent for this purpose. The groundelectrode may be made-of spark-resisting alloy; since it can beseparately formed from the shell or integrally formed therewith. Ineither event, the material should be sufficiently ductile ormalleable toeliminate any spring-action when it is deformed, com- 40 pressed orbent, and to cause it to remain set in its adjusted position or shape.

When the gap between thesparking surfaces on the electrodes becomesexcessive from use or wear, an ordinary hammer of suitable size may be 5usedto pound down the portion 21 of the strip forming the electrode 24.A templet or strip a, indicated by dotted lines in Fig. 2, of a correctthickness to correspond to the optimum gap between the electrodesfi maybe inserted between them while the portion 21 of the strip formingelectrode 24 is hammered down to provide the proper gap; On account ofthe softness or lack of spring in the metal forming the electrode 24,vthe central portion 21 will be set, as indicated face on its inner sidewill be brought down to the correct distance from the sparking face ofthe center electrode, without resulting in any substantial recession ofthe sparking face on portion 21 from the strip a or the sparking face Idof the inner center electrode. By hammering down the entire centralportion 21 and the use of 'a templet, the normal parallelism of thesparking-faces, which are perpendicular to the axis of the electrode I2, will be retained. By forming the ground electrode of metal which willremain set in the position in which it is hammered, it makes it possibleto provide a spark plug in which the sparking faceof the centerelectrode is shielded by the ground electrode to prevent direct contactof the flame with the sparking face of the inner electrode and to easilyvary or adjust the sparking faces-for the correct or most efllcientspark gap.

In the event that the gapbetweenthe sparking faces of the electrodes istoo small, after the electrode 24 has been applied, the gap may beincreased by screwing out the assembly consisting of the electrode I2,sleeves I5, 22 and ring ll slightly, inserting a templet a and thenscrewing 'down the said assembly. Usually, use of the plug increases thegap and the adjustment required is a decrease of the gap, which is doneby hammering the portion 21 of electrode 24, as before described.

In low output engines, the diameter of the cylindrical end l3 of theinner electrode is smaller than the diameter used in high outputengines.

In the modification illustrated in Figs l and 5, the electrode 24 on theshell is made of metal having the ductile and springless propertieshereinbefore described and comprises a central portion 21* of sufficientarea to extend over the sparking face on the large cylindrical .end I3of the central electrode il of a spark plug fora high output engine. Theends Mi of the strip 24 are brazed or welded in recesses in the end ofthe shell se In this modification the electrode 24* is normally fiat andits entire flat central portion is adapted to be deflected or hammeredtdwardthe sparking face M of the inner electrode, as indicated by dottedlines in Fig. 4, so asto maintain parallelism between the sparking"surfaces. In 'high output engines, it is desired to terminate thecentral electrode inwardly of the end of the shell as shown. In thiscase, the central portion 22 is deflected downwardly by a suitablehammer to keep its inner face in parallelism with the sparking face itand the metal between the central portion and the end portions 25 isdeflected downwardly and stretched, as indicated at 28 While this isdonea templet may be inserted between the sparking faces of the electrodesto arrest and set the central portion of the strip the correctdistance'from the sparking face I4 and provide the correct spark gap.

Fig. 6 illustrates a modified form of ground electrode of ductile ormalleable metal having the same properties as those hereinbeforedescribed and which comprises a circumferential rim 30 which is brazedor welded, as indicated at 3!, to the shell ill"; a central portion 32adapted to extend over and shield the sparking face on the end of theinner electrode 82', and a series of connecting arms 33 between theannular portion 30 and the central portion 3!. The central portion 32may be deflected by a hammer, as hereinbeioredescribed, when thesparking faces are to be brought together to compensate for wear. In this form of the invention the arms 33 are offset 75 adjacent the annularportion 30 to permit the deformation of the metal while the centralportion is being hammered to form the desired sparkgap.

The invention exemplifies a spark plug with an electrode on the shellwhich shields the sparking face of the central electrode from directcontact with the cylinder flame and isreadily and accurately variable toprovide the optimum spark-gap.

The invention also provides for variation of the spark-gap by hammering,which results in resetting or adjusting the metal'without spring-action.The invention also provides for embodying these features in groundelectrodes'of different forms. The invention also provides a groundelectrode having these characteristics which provide for recession ofthe spark-plug gap into the shell for high output engines.

The invention also provides a ground electrode having, thesecharacteristics which may be separately formed'from the shell, sothatthey may be made of spark-resisting metal, although it is to beunderstood that in some instances the invention may be applied to groundelectrodes which, for cheapness in manufacture, are integrally formedwith the shell.

stricted to the details set forth, since these may be modified withinthe scope of the appended claims, without departing from the-spirit andscope of the invention.

Having thus described the invention, what I claim as new and desire tosecure by Letters Patent is:

1. A spark. plug comprising a shell-provided with means whereby it maybe secured to an engine-casing, an inner electrode in the shell having aflat sparking-face at its inner end, and a flat strip forming a coactingelectrode, bridging the inner end of the shell, formed separately fromand having both of its ends permanently bonded to the shell andcomprising an integral central portion having a substantially flatsparking-face parallel with the sparking-face on the inner electrode,said strip being formed of malleable or duetile metal which can bepounded or deflected to- Ward the sparking-face on the innerelectrode tovary the gap between the sparking-faces by deformation between itscentral portion and both of its bonded ends, so that the central portionwill remain set and maintain the parallelism between the sparking-faces.

the shell and comprising an integral central por-,

tion having a substantially flat sparking-face parallel with thesparking-face on the inner electrode and longitudinally extendingportions between the central portion and the bonded portion,

said. strip being formed of malleable or ductile metal which can bepounded or deflected toward the'sparking face on the inner electrode tovary the gap between the sparkingafaces by deformations in thelongitudinally extending portions, so that the central portion willremain set and maintain the parallelismbetween the sparking-faces.

3. A spark plug comprising a shell providedwith means whereby it may besecured to an engine-casing, an inner electrode in, and terminatinginwardly of, the shell having a flat sparking-face at its inner-end, anda transversely straight flat strip forming a coacting electrode,

bridging the inner end of the shell, formed separately from and havingboth of its ends permanently bonded to the shell and comprising anintegral central portion having a. substantially fiat sparking-facenarallel with the sparking-face on the inner electrode, said strip beingformed of malleable or ductile metal which can be pounded or deflectedtoward the sparking-face on the inner electrodeto vary the gap betweenthesparkingfaces by deformations between its central portion and both ofits bonded ends, so that the central portion will remain set andmaintain the paral- B lelism between the sparking-faces.

CECIL R. BENTON.

